1. Field of the Invention
The present invention relates to an optical fiber cable, and particularly to an optical fiber ribbon cable with a laminated structure.
2. Description of Related Art
Optical fibers are now used in a variety of telecommunication applications because of small physical size and high bandwidth capacity. An optical fiber cable typically contains a number of individual optical fibers. Different configurations of optical fibers in the cables leads to a variety of cable types, including loose-tube cables, tight-buffered cables, and optical fiber ribbons.
It is not uncommon for an optical fiber cable containing one or more optical fibers to undergo rough handling or to be exposed to a physical environment that stresses or crushes the fiber or fibers within the cable. For example, an optical fiber contained within an optical fiber cable can experience stress and strain when the cable is bended or stretched during winding on a reel for purposes of storage. An optical fiber cable pinched between other cable components may be subject to mechanical stresses due to differences in coefficients of thermal expansion between the optical fiber and the other components of the cable, such as a tube containing the fiber, or protective layers inside an optical fiber ribbon cable.
A variety of techniques have been developed to hold and protect individual fibers from damage. For example, fibers are frequently encased in a jacket or other protective material. In addition, individual fibers are often grouped together to provide a cable capable of carrying increased amounts of information.
Cylindrical optical fiber cables usually employ additional protective layers to relieve stochastic strain, stress, crush loading, impact, or abrasive forces exerted thereon. These protective layers commonly include buffer tubes/layers, strength members, filler members in loose-tube type cables, and thick jackets made of polyvinyl chloride (PVC) or other appropriate materials.
However, in the case of ribbon type optical fiber cables, some of the more ordinary protective means, such as filler members used in the cylindrical optical fiber cables become unfeasible. Instead, other protective elements, such as buffers or strength members, can be applied around individual optical fibers contained in a ribbon cable.
Individual optical fibers have been woven into sheets, aiming to provide a workable solution to the above-discussed problems. For example, as disclosed in U.S. Pat. Nos. 5,524,679, 5,469,895, 5,280,558 and 5,256,468, optical fibers have been woven into a supporting structure. Once completed, the woven, grid-like mat can be coated with various types of protective material, such as an elastomer or a rubber epoxy, to form a flexible sheet with the optical fibers embedded therein. Alternatively, the structure can be coated or embedded in a rigid material, such as epoxy, to form a hard or rigid, grid-like structure.
Although such flexible or rigid, grid-like mat structures can achieve good tensile resistance, they unavoidably result in a highly complicated manufacture with attendant high costs. Moreover, such a solution does not work well to resist impact, crush and abrasion.
Another related prior art for solving the above-discussed problems is disclosed in U.S. Pat. No. 4,679,897, as shown in FIG. 3. An optical fiber ribbon cable combination 1 includes a pair of plastic tapes 14, a ribbon 10 consisting of a plurality of optical fibers 15, and a pair of plastic insulated copper conductors 12. The ribbon 10 is disposed between the conductors 12 and the conductors 12 extend lengthwise of the tape along with the ribbon 10. The ribbon 10 and the conductors 12 are sandwiched between the tapes 14. The ribbon 10 is loosely housed within an elongate compartment defined by the conductors 12 and the tapes 14. When a tensile force is applied to the cable combination 1, the conductors 12 and the tape 14 help carrying the tensile load, sparing the ribbon 10 from carrying the whole tensile load.
However, the conductors 12 can be easily disconnected from the tapes 14 under the tensile force applied thereon since the conductors 12 are only attached to the tapes 14 by fusion bonding. Furthermore, since the ribbon 10 is loosely housed in the compartment between the conductors 12, the ribbon 10 is apt to slide out of the cable assembly 1 when the conductors 12 are disconnected from the tapes 14, thereby exposing the ribbon 10 and its optical fibers 15 to serious damage.
A main object of the present invention is to provide a low-cost, flexible fiber ribbon cable having good resistance against crushing, impact, abrasion and tensile loads.
An optical fiber ribbon assembly in accordance with one aspect of the present invention, comprises a plurality of aligned optical fibers and a laminated structure surrounding the optical fibers. The laminated structure comprises a clear polyvinyl chloride (PVC) extrusion layer bonding the fibers together and a pair of Kapton layers enclosing the PVC extrusion layer. An aramid laminate may substitute the Kapton layers to provide flexible protection to the subassembly of the PVC extrusion layer and the optical fibers. Additional KEVLAR members may be aligned with the fibers and may also be embedded in the PVC extrusion layer and the laminated Kapton layers, thereby providing the fibers with additional protection from outside tensile loads.